I notice that my 2001 ML320 lose power when it rain hard and little flood. I inspected the muffler but no leak. any ideas??? Thanks

I don't know exactly, but in my case, one of the coil packs had a micro crack, thats why every time it rained the car misfired, lost power, or sometimes one of the cylinders would shut off completely.

sounds like you would need a scan tool and a garden hose. good luck.